<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    :root {
      --my-cool-background: #73a4f4;
    }

    p {
      color: var(--my-cool-background);
      max-width: 600px;
      margin: 20px auto;
      font-size: 2em;
    }

    #foo {
      background-color: var(--my-cool-background);
    }

    body {
      text-align: center;
      line-height: 1.6;
    }
  </style>
</head>
<body>
  <div id="foo">
    <h1>Hello</h1>
  </div>
  
  <div>
    <p>
      More text inside another div. This also will have the nice light blue color, but not as a background, but as text color.
    </p>
  </div>
</body>
</html>